Wattmeter



Sept. 26, 1950 E. MITTELMANN WATTMETER Filed April 23, 1946 memellevfer' INVENTOR.

Mfi dsc/l/alor ac. mvoar vanes Patented Sept. 26, 1950 UNITED STATESPATENT, OFFICE WATTMETER Eugene Mittelmann, Chicago, Ill.

Application April 23, 1946, Serial No. 664,146 Y 14 Claims. 1

The present invention relates to a circuit arrangement and apparatus formeasuring the power absorbed by the load only in a high frequency field.

In high frequency circuits, particularly such circuits now commonly inuse for heating materials with high frequency energy, it is .desired toobtain an indication of the power absorbed by such material. It has beencommon to provide measuring devices which indicate the total poweroutput of a high frequency generator which is supplying energy to heatmaterial by either a capacitive or inductive apparatus. The total poweroutput, however, may be quite different from the power absorbed. In myprior Patent Re. 22,258 I disclosed means capable of measuring the powerabsorbed. Such means, however, requires certain calibratingmanipulations wh ic it is desired to avoid.

In that prior patent, it was pointed out that the secondary resonancecircuit in which the heater was included can be denoted by twoequivalent circuits, one for no-load conditions and the other for loadconditions, the no-load condition being denoted by a circuit having aninductance, a capacitance and a single resistor R in parallel with eachother and connected across a source of high frequency. The loadcondition is denoted by the same circuit to which a resistor R1 is addedin paralled with the resistor R0. On

the basis of such circuits it was shown it is possible to calibrate agalvanometer shunting resistor so that for different loads the resistorcan be adjusted to cause the galvanometer to indicate the power absorbedby the load. This is not entirely satisfactory, however, because it re--quires the adjustment of the shunt resistor for each difierent load. Mypresent invention overcomes that difliculty and makes it possible tometer the power absorbed without adjusting the meter on changes in load.

Other and further objects of the present invention subsequently willbecome apparent by reference to the following description taken inconnection with the accompanying drawing wherein:

Figure 1 illustrates a circuit arrangement and apparatus for indicatingdirectly the power absorbed by a load in a high frequency circuit;

Figure 2 graphically illustrates the linear relationship between thedirect current plate voltage for a high frequency oscillator and thehigh frequency tank circuit voltage for different loads;

Figure 3 is another embodiment whereby the wherein R0 is the equivalentno-load parallel loss resistance of the unloaded tank circuit, ea isthat value of no-load resonant voltage across the resistance required toproduce the no-load (power loss in said resistance, R1 is the equivalentparallel load loss resistance, and er is that value of resonant loadvoltage across the resistances required to produce the load power lossin the resistances R0 and R1.

The amount of power absorbed by the external load is equal to 1 ea-"6His T for any actual value E1 of the working voltage across the tankcircuit of the high frequency oscillator. In place of co and er theactual noload oscillator tank circuit voltage E0 and the actual voltageE1 may be substituted, if E1 is measured at the same value of directcurrent plate supply voltage as E0, and the following relation istherefore obtained P=R;(E1E0"E12) This relationship may be used todesign a power absorption wattmeter which will not require a calibratingadjustment for each different value of power absorbing load resistanceR1.

, A direct linear relation exists between E0 and the direct currentanode voltage Eb of the oscillator, and Equation 3 can be replaced bythe equation This linear relationship will become evident by referringto Figure 2 wherein the direct current anode or plate supply voltage isplotted as a func- 3 tion of the deflection of a vacuum tube voltmeterconnected across the tank circuit of an oscillator, such as A, underno-load conditions indicated by the curve D and under different loadconditions indicated by the curves E and F. It is apparent that thevoltages E and E1 bear a direct linear relation to the direct currentplate voltage Eb, and hence it is possible to use this direct currentplate voltage as an indication or measurement of the no-load voltage En.

In Figure l rectangle A denotes a high irequency vacuum tube oscillatorhaving an output tank circuit including an inductor A2 and a parallelconnected capacitor A8, the energy absorbing load or reactive heaterbeing coupled to the inductor A2. Also coupled to the output inductor A2is a pick-up coil Bi connected in a circuit containing a rectifier B2, apair of generator or dynamo field coils B3 and B4 and an armature B5 ofa motor having permanent magnet pole pieces B5. The field winding BI isassociated with an armature B1 connected in series with the armature B8which is associated with the field coil B3. A resistor B8, in serieswith armatures B1 and B8, is provided with an adjustable contact whichis connected to a voltmeter Bill. The armature BB is driven by anarmature CI of a motor having a permanent magnet pole piece C2. Thearmature Cl is connected in series with a resistor C3 and is supplied bycurrent obtained from the direct current anode supply circuit of thehigh frequency oscillator A. The armatures B5 and B1 are mechanicallyconnected together.

A rectifier B2, connected in series with the pick-up coil Bl supplies tothe field coils BI and 34a current which is proportional to the highfrequency load voltage E1 of the tank circuit of the oscillator A. Thearmature B5, being energized by the current supplied by the rectifierB2, drives the armature B1 so that voltage generated thereby isproportional to E1. The armature B8 is driven by the armature Cl, whichis energized by a current proportional to Es, but the field winding B3is energized by a current proportional to E1. Hence, the output voltageor current of the armature B8 is proportional to ElEb. The armature B8is connected in voltage opposition to the armature Bl so that thevoltage appearing across the resistor B9 is proportional to EiEt-Ei. Thevoltmeter Bill is connected across the resistor or voltage B9 and,therefore, indicates, in accordance with Equation 4, the amount of highfrequency power absorbed in the load. This indication will be correctfor any arbitrary or changing value of plate supply voltage and for anyarbitrary or changing load value.

Another circuit arrangement is illustrated in Figure 3 wherein there hasbeen shown a pushpull high frequency oscillator employing a pair ofvacuum tubes GI and G2 having their cathodes connected to the negativeside of a. source of anode potential. The positive side of the anodesource of potential is connected to ground and to the midpoint of thetank circuit inductor G8 which may be bridged by a tuning capacitor G4.By suitable capacitors G5 and G8 interconnected by a choke coil G1,energy is obtained from suitable taps on the tank inductor GI for theexcitation of the grids of the tubes GI and G2. This circuit arrangementis merely one example of a suitable type of high frequency vacuum tubeoscillator commonly used for supplying high frequency energy for heatingpurposes. A rectifier HI having a pair of anodes and a cathode isarranged to have its anodes connected to opposite ends of the tankcircuit coil G8. A suitable filter capacitor H2 is connected between thecathode of the rectifier HI and the midpoint of the tank inductor G8. Adouble or twin dynamometer indicating instrument-is energized bycurrents proportional to the direct current plate voltage supplied tothe oscillator and to currents proportional to the resonant voltageacross the tank circuit. The double dynamometer has two armature coils Jl and J2 and two field coils J8 and JI. The armature J I is connected inseries with a resistor J5 so that the armature is energized by currentproportional to the direct current voltage supplied to the anodes of theoscillator tubes GI and G2. The

two field coils J8 and J4 are connected in parallel with each other andin series with the armature coil J2. This circuit is energized from therectifier HI which delivers current proportional to E1 which is the highfrequency voltage appearing across the tank circuit inductor G3. The twoarmatures Jl and J2 are mechanically connected together and inopposition to operate the common indicator N so that the resultanttorque, and hence the deflection of the needle is proportional to theterm Emit-E1). The armature coil J2 has half the number of turns of thecoil Jl since the current proportional to E1 is equally divided betweenthe field coils J3 and J4.

Figure 4 shows another manner in which power may be taken from the tankcoil A2 of an oscillator A and converted by the rectifier HI to supply adirect current proportional to E1. In this circuit arrangement therectifier cathode Hi is connected to a choke coil H3 which in turn isconnected through a capacitor H4 to ground. The common juncture betweenthe capacitor and the choke coil is connected to the field coil J 5 of adynamometer having two armature coils J6 and J1. The field coil J! isconnected in series with the one armature coil J 8 which in turn isconnected to ground. The other armature coil J! is connected betweenground and the negative side of the anode potential for the oscillatorA. Electrodynamically, the meter produces a torque proportional to theproduct E1(Eo-E1).

Figure 5 shows a rectifier HI coupled by a plurality of capacitors HIand H8 to suitable tapped positions on the tank inductor A2 of theoscillator A. The resistor H1 is connected between the anodes ot therectifier HI. A choke inductor H8 is connected in the cathode lead tothe rectifier HI. An output resistor H9 is connected between the cathodeand the midpoint on the resistor H1. A suitable filter capacitor HID isconnected across the resistor H9. Another choke coil Hll is connectedbetween the resistor H8 and the midpoint on the resistor H1. The voltagedeveloped across the resistor H9 is proportional to E1. This resistor isconnected to the field coil J! of a dynamometer having an armature J9.The armature J! is energized by the voltage difference between thevoltage Eo developed across a resistor J H) in the plate supply circuitfor the oscillator and the voltage E1 supplied by the rectifier HI. Thevoltage appearing across the resistor J I8 is opposed by the voltageappearing across resistor H8 so that the effective voltage supplied tothe armature coil J! of the dynamometer is equal to Eo-lh.Electrodynamically the dynamometer multiples these voltages tobrated bydetermining a single value of Bi tor any arbitrary value of the voltageEo. Having determined this position on the instrument dial all otherpoints or the scale may then be computed so that the indication is inaccordance with the requirements of the power equation.

While for the purpose of describing and illustrating the presentinvention certain circuit arrangements and embodiments have been shown,it is to be understood that the invention is not to be limited therebysince such variations and modifications are contemplated as may becommensurate with the spirit and scope of the invention set iortn in theiollowing claims.

This invention is hereby claimed as follows:

i. The method of measuring the power absorbed by a load from the outputcircuit of a high frequency oscillator comprising deriving a iorcedirectly proportional to liii, the voltage or the output circuit underload, deriving another force directly proportional to E0 the no-ioadvoltage 01 tne output circuit, comparing said forces and combining thedinerence with the nrst force to produce a force proportional to thepower absorbed in said load.

a. A dev ce for measuring the power absorbed by material in a reactiveheater coupled to the output circuit 0f 9. high frequency electronicDUDE generator comprising means for developing a voltage proportional toan, means for developing a voltage proportional to m,- and means i'orapplying said voltages to an indicating means the denecting force ofwhich is proportional to EiiEt-lh) to cause said indicating means toindlcate the power absorbed by said material in said reactive heaterwhere Ei is the voltage of the high frequency power source 'under loadand Lb is proportional to the plate supply voltage 01 the high frequencytube generator.

3. A device for measuring the power absorbed by loads of diii'erentimpedance values from the output circuit of a high frequency vacuum tubeoscillator comprising means for developing a voltage proportional to E1,means for developing a voltage proportional to Eb, and means forapplying said voltages to an electrodynamic indicating means energizedin accordance with E1(EbEl) where E; is proportional to the workingvoltage 01 the tank circuit of the oscillator under load and Eb isproportional to the direct current plate voltage of the oscillator at noload.

4. A device for measuring the mower absorbed by the load in the outputcircuit of a high frequency oscillator comprising a pair of generators,means for driving the armature of one generator at a speed directlyrelated to the working voltage of the loaded power circuit, means fordriving the armature of the other generator at a speed directly relatedto the no-load voltage of said output circuit, means for exciting bothgenerators in accordance with the working voltage of the loaded outputcircuit, and means for comparing the outputs of said generators and forindicating the difference therebetween.

5. A device for measuring the power absorbed by a load in the outputcircuit of a high frequency oscillator comprising a pair of generators,a direct current motor for driving the armature of one generator at aspeed proportional to the working voltage of the loaded output-circuit,a second direct current motor for driving the armature of the othergenerator ata speed proportional to the no-load voltage of said outputcircuit, means for exciting both generators with current proportional tothe working voltage of the loaded output circuit, circuit means forconnecting the outputs of said generators in opposition, and a meter torindicating the difference.

6. A device tor measuring the power absorbed by a load in the outputcircuit of a high frequency oscillator heating apparatus comprising apair of direct current generators, a constant field direct current motorhaving its armature energized in accordance with the working voltage oithe loaded output circuit for driving the arma ture of one of saidgenerators, a second constant field direct current motor having itsarmature energized in accordance with the no-load voltage of said outputcircuit for driving the armature oi the other generator, means forexciting both generators with direct current proportional to the workingvoltage of the loaded output circuit, and means for indicating the'difierence between the outputs of said generators.

7. A device for measuring the power absorbed by a load in the outputcircuit of a high frequency heating apparatus comprising a pair ofdirect current generators, a constant field direct current motor fordriving the armature of one or said generators, said motor having itsarmature energized by current proportional to the working voltage of theloaded output circuit, a constant field direct current motor for drivingthe armature of the other generator, said second motor having itsarmature energized with current proportional to the no-load voltage ofsaid output circuit, means including a rectifier energized from theoutput circuit of said oscillator for supplying exciting current to bothgenerators, means for connecting the outputs of said generators inopposition, and a, direct current meter ior indicating the powerdifference therebetween.

8. A device for measuring the.power absorbed by a load from the outputcircuit of a high frequency electronic tube oscillator comprising anelectrodynamic meter, means for supplying thereto current directlyproportional to the voltage of the output circuit under load, and meansfor supplying thereto current directly proportional to the plate supplyvoltage of the electronic tube oscillator.

9. A device for measuring the power absorbed by materials to whichheating energy is supplied from the high frequency output circuit of anelectronic tube oscillator having a direct current plate supply circuit,said device comprising a direct current electrodynamic meter having aplurality of windings, rectifying means for supp y direct current fromthe output circuit to certain of said windings of said meter, and meansfor supplying to the remainder of said windings direct current from theplate supply of the oscillator of said high frequency heating apparatus.

10. A device for measuring the power absorbed by a load from the highfrequency tank circuit of an electronic tube oscillator having a platesupply circuit comprising a direct current electrodynamic meter having aplurality of windings, a rectifier connected to the tank circuit of saidhigh frequency oscillator, means interconnecting the output of saidrectifier with certain of said windings of said meter, and means forsupply-.

ing to the remaining 01 said windings of said meter direct current fromthe plate supply circuit 01' said oscillator, said certain and remainingwindings being poled for electrodynamic opposition.

11. An arrangement for indicating the power absorbed by a. loadenergized by the output circuit of a high frequency oscillatorcomprising a direct current indicating instrument having two sets offield and armature windings and a common indicator, a rectifierconnected to receive energy from said output circuit and to supplyrectified energy to said field windings, means for energizing one ofsaid armature windings with direct current energy received from saidrectifier, and means for energizing the other of said armature windingswith direct current proportional to the anode voltage of saidoscillator, said sets of windings being so poled that one set acts onthe indicator in opposition to the other set.

12. An arrangement for indicating the power absorbed by a load energizedfrom the high trequen cy output circuit of an electronic tube oscillatorcomprising a direct current instrument having a field winding and twoarmature windings. a rectifier connected to receive energy from saidoutput circuit and to supply rectified energy to said field winding andone of said armature windings, and means for energizing the otherarmature winding with direct current proportional to the anode voltageof said oscillator.

13. An arrangement for indicating the power absorbed by a load energizedfrom the high frequency output circuit of an electronic tube oscillatorcomprising a wattmeter having plural actuating windings, means forapplying to one 8 winding of said wattmeter a voltage directlyroportional to the voltage oi said output circuit, and means constantlycomparing said applied voltage with the anode voltage of said oscillatorand energizing another wattrneter winding with the diil'erence voltage.

14. An arrangement for indicating the power absorbed by a load energizedfrom the high irequency output circuit of an electronic tube oscillatorcomprising a direct current wattmeter having a pair 01' actuatingwindings, a rectifier energized from said output circuit, meansconnecting the output of said rectifier to both windings of saidwattmeter to apply a voltage thereto, circuit means applying to onewinding 0! said wattmeter, in opposition to the rectified voltage, a

voltage derived from the anode supply for said oscillator.

EUGENE MI'ITEIMANN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 22,258 Mitteimann Jan. 26,1943 2,434,544 Boykin Jan. 13, 1948

